1. Field of the Invention
The present invention relates to the relay of signals in a wireless network.
2. Description of the Related Art
In a wireless network, such as an ad hoc network, in which a signal is relayed from a source node to a destination node through a plurality of intermediate nodes, indiscriminately routed signals are apt to collide or interfere, causing transmission errors. Japanese Unexamined Patent Application Publication No. 2001-244983 therefore equips the intermediate nodes with directional beam antennas; by measuring the strength of signals received from various directions and keeping a table of signal strengths and directions, an intermediate node can select a neighboring node that will minimize both radio interference and the number of hops to the destination, and beam its signal to the selected node. Beaming signals in this way prevents transmission errors due to interference, and reduces power consumption as well. The same directional beam antenna is used for both transmitting and receiving, the beam direction being changed by, for example, electronic control of scanning intervals across a phased array of antenna elements.
A drawback of this arrangement is that the antenna cannot be used for transmitting and receiving simultaneously. Each continuously received signal packet must therefore be stored in a buffer memory. After the entire packet has been received, the antenna beam direction is switched, the stored signal is read from the buffer, and transmission begins. The relay process accordingly includes a delay at least equal to the length of the packet. Switching the antenna direction, converting the received signal to a form storable in the buffer, and switching the buffer between read and write access also adds slightly to the delay.
The delay accumulates from one relay node to the next. Particularly in a network employing low-power signal transmission, since the number of hops on a route tends to be large, the cumulative delay may become substantial. If the transmitted signal is an audio or video signal, the delay may seriously impair the quality of the received sound or picture.